1. Field of the Invention
The present invention relates to apparatus for the taking of liquid samples from a mixture of liquid and solids.
2. Description of the Prior Art
The chemical industry in particular is often involved with processes which use reaction media comprised of a mixture of liquid and solid. In such cases, it is often a matter of interest to be able to analyze the liquid phase of the mixture in such manner as to be able to trace the progress of the reaction, or to be able to control the reaction.
A typical example is the production of phosphoric acid by a wet process, wherein the phosphate ore is subjected to attack by a strong acid. In the case of an attack sequence using sulfuric acid, the resulting product is a slurry including a liquid phase which comprises, in particular, the product phosphoric acid, and a solid phase which contains, in particular, calcium sulfate.
Now, in order to ensure that the reaction takes place in a satisfactory manner, it is very important to maintain the content of sulfate ions in the reaction medium within a well defined range. For that purpose, it is therefore necessary to ascertain the concentration of sulfate ions quickly and as frequently as may be required.
French Patent No. 2,090,541 describes apparatus for the automatic continuous analysis of the H.sub.2 SO.sub.4 in phosphoric acid, which operates on the strong acid resulting from filtration of the attack slurry.
The disadvantage of such an apparatus is precisely in the fact that it analyzes an acid resulting from the filtration operation. Indeed, it is highly probable that analysis carried out utilizing such apparatus does not precisely reflect the conditions prevailing in the attack vessel. Thus, in the filtration operation, various phenomena may occur, which modify the composition of the acid. Moreover, it is preferable to analyze the acid directly within the attack vessel rather than at the outlet of the filter to provide a much shorter response time, thus affording the possibility of immediate intervention, if needed.
However, it has been found to be difficult to develop an apparatus for the taking of samples of acid directly from the reaction medium, for the purpose of effecting the analysis thereof. In fact, to be suitable for industrial use, such an apparatus must be adapted to resist corrosion, it must operate without requiring frequent cleaning and therefore it must be so designed as not to be rapidly fouled by the attack slurry. In addition, the liquid sample must be as free from any solid impurity as possible, in order to avoid problems in carrying out any analysis.